FR3083739A1 - Optical component with scratch-resistant anti-reflective coating and method of making it - Google Patents

Abstract

The present invention proposes an optical component (10) which comprises a substrate (1) provided with a stack of layers (2) comprising a plurality of successive layers of different materials and with different refractive indices, which defines an antireflection coating. The layers of the stack of layers (2) are made of at least three different materials or combinations of materials, so that the stack of layers (2) comprises at least one layer of a first type, of a second type and of a third type, with at least three different refractive indices. A layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type. A top layer and a second top layer are provided. The upper layer (7) is a layer of the second type (3) and the second upper layer is a layer of the first type (4) and therefore has a refractive index which is higher than the refractive index of the upper layer . The stack of layers (2) comprises at least one additional layer which is arranged under the two upper layers of the stack of layers (2) and which is a layer of the third type (5) and thus has a lower refractive index to the refractive indices of the two upper layers. Reference: figure 1

Description

Description

Title of the invention: Optical component with scratch-resistant anti-reflective coating and its manufacturing process Field of the invention The invention relates generally to an optical component provided with an anti-reflective coating, and more particularly an optical component provided with an anti-reflective coating with a substrate, as well as a method for coating the optical component and its use.

Background of the invention [0003] Anti-reflective coatings are today widely used to improve the transmission of transparent substrates such as observation windows, and on the other hand to reduce disturbing reflections on the substrate . However, depending on the intended use of the support, the anti-reflective coating may be subjected to high wear loads. For example, an exterior coating of a vehicle windshield will be subject to particles of sand and dust that collide at a high speed during travel, which can wear down the coating over time. In addition, a special charge occurs for these windshields when a wiper passes over the dirty windshield. The particles of sand and dust are not only transported on the windshield, but they are at the same time pressed against the windshield by the rubber lip of the wiper. This can cause long scratches in the coating.

Scratches and other deterioration cause haze due to the diffusion of light, reduce the anti-reflective effect of the coating by altering it and thus go against the objective of an anti-reflection coating.

This is why it is necessary to have an anti-reflective coating having a high resistance to scratching and abrasion.

The abrasion or the formation of scratches is generally caused by an abrasive medium, such as a grain of sand, causing cracks of the order of a nanometer in the material by moving laterally on the surface or following a normal impact. Most of the time, the cracks do not become visible and are not visually noticeable before other cracks occur along the edges of the cracks, which scatter light, or even before delamination occurs. The behavior of a surface to form cracks depends on different parameters such as Young's modulus, surface roughness, brittleness, stress near the surface or the tendency of the two materials involved (substrate and abrasive medium) to form covalent bonds. The hardness of the substrate, measured using an indenter test method (eg Knoop hardness), is only one of the many parameters that influence, but one of the most important.

From document US 2005/0074591 A1, a transparent substrate is known with an abrasion resistant anti-reflective coating. The anti-reflective coating is made up of four layers alternating between high and low refractive indices. The low refractive index layers are made of silicon oxide (SiO ₂ ), the high refractive index layers are made of silicon nitride (Si ₃ N ₄ ) or tin oxide (SnO ₂ ). The upper layer of the stack of layers is formed by a layer with a low refractive index. The disadvantage is that the silicon oxide layer with low refractive index is very soft compared to materials with high refractive index, in particular compared to Si ₃ N ₄ . Consequently, it is above all the upper layer which can still wear out quickly. When the top layer is worn, a high index layer forms the surface. In the worst case, this leads to an inversion of the anti-reflection effect, so that the layer then acts rather as a dielectric mirror (semi-transparent mirror) at the location of the scratch.

There are optical applications in different infrared ranges of the electromagnetic spectrum. For use in a single spectral range, materials such as sapphire, germanium or silicon are commonly used. However, if an optical component is intended to operate in several ranges of the electromagnetic spectrum at the same time, for example [0009] - in the range of visible wavelengths of between approximately 400 nm and approximately 650 nm, preferably between approximately 450 nm and around 650 nm, [0010] at a laser wavelength in the near infrared of between 1000 nm and

600 nm, for example at laser wavelengths of 1,053 nm, 1,064 nm, 1,535 nm or 1,550 nm, [0011] - in the mid infrared between 3,500 nm and 5,000 nm, and [0012] in the far infrared between 7,500 nm and 12,000 nm, there are only a few materials available as substrate material for the optical component.

A transmission for a wavelength in the spectrum of the near infrared between 1000 nm and 1600 nm may be necessary for a LIDAR application, also called rangefinder application. Rangefinders which contain phosphate glass doped with ytterbium and erbium as an active laser medium, for example LG940, LG950 or LG960 (manufactured by SCHOTT AG), emit at 1535 nm.

Zinc sulfide and zinc selenide are examples of materials suitable for applications of this type. Most of the materials used for infrared spectral applications do not transmit in at least one or more of the four ranges listed above. Although sapphire can be used in visible, near and medium infrared, it is no longer transmitted sif beyond 6000 nm. Germanium or silicon, which are transmissive in the far infrared, cannot be used as a window in the visible range. The choice of substrate materials to use, from visible to far infrared, is very limited, as is the availability of the desired refractive indices of possible substrate materials.

However, these materials are often soft or not very resistant to abrasion and brittle and have only a medium to high refractive index (1.7 to 2.5). The rather high refractive index is associated with a high reflectivity of the surface made of such a material. This is why an anti-reflective coating is necessary in such cases. Again, there are only a small number of materials available for this purpose. High index coating materials which are considered for the anti-reflective coating include for example zinc sulfide (ZnS), hafnium oxide (HfO ₂ ), scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ) and cerium oxide (CeO ₂ ). The low index materials which are taken into account for the anti-reflective coating are for example barium fluoride (BaL ₂ ), calcium fluoride (CaL ₂ ), cerium fluoride (CeL ₃ ), lanthanum fluoride ( LaL ₃ ), neodymium fluoride (NdL ₃ ), ytterbium fluoride (YbL ₃ ), magnesium fluoride (MgL ₂ ), aluminum fluoride (A1L ₃ ), dysprosium fluoride (DyL ₃ ) and yttrium fluoride (YL ₃ ).

A particular drawback of materials with a low refractive index is the fact that they are soft. For anti-reflective coatings, it is generally necessary to apply a layer with a low refractive index as the last outer layer. This is necessary in particular if the anti-reflective coating is complex, that is to say if it has a strong anti-reflective effect (substrate materials with a high refractive index) or if it must be effective in a plurality of spectral ranges. Therefore, a fluoride layer is often used as the top layer. However, it is in particular materials with a low refractive index which have the drawback of being soft and therefore of not resisting scratches. In optical embodiments, an attempt is generally made to compensate for the absence of scratch resistance at least in part by a very large layer thickness of the last layer or by the fact that the optical efficiency of the optical coating depends to a small extent. the layer thickness of the top layer.

The reduced scratch resistance of the flexible upper layer is a drawback when the corresponding optical component is used outside, for example as a sensor window in military vehicles and aircraft. In desert areas, for example, the disadvantage of insufficient scratch resistance is exacerbated by the high sand content of the air. Therefore, the fluoride layers of the above listed compounds are not suitable for such operating conditions. Some of the oxides listed above are also unsuitable for such uses, due to their solubility in water.

In order to protect the surfaces of the optical elements against scratches, it is known to provide the surface with a hard coating. A hard anti-reflective coating is known from document EP 2492251 A1.

In general, infrared materials with a high refractive index, such as germanium, can receive, as an anti-reflective coating, an extremely hard layer of carbon (DLC), of diamond type, because the refractive index of the substrate is significantly higher than that of the layer. To obtain an anti-reflective effect for the surface of a substrate with a single layer relative to air as an adjacent medium, as is the case in certain applications using DLC, for example on germanium, or using a layer of fluoride (eg MgE ₂ ) on some glasses, the refractive index of the layer should ideally be close to the square root of the refractive index of the substrate. However, in the case of materials whose refractive index is in the range of that of ZnS or ZnSe and below, the DLC is not suitable for many spectral ranges, including the visible range.

Brief description of the invention The present invention aims to provide an optical component with an anti-reflective coating which is suitable for use in multiple spectral ranges and which has abrasion resistance improved compared to prior art coatings.

This object is achieved by the subject of the independent claims. Advantageous embodiments and improvements of the invention are defined in the dependent claims.

The optical component according to the invention comprises a substrate provided with a stack of layers which comprises a plurality of successive layers of different materials and with different refractive indices, which defines an anti-reflective coating, in which the layers of the 'stack consist of at least three different materials or combinations of materials, so that the stack of layers comprises at least one layer of a first type, a second type and a third type, with at least three different refractive indices, where a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than that of a layer of the second type; and in which an upper layer and a second upper layer are provided, knowing that the upper layer is a layer of the second type and the second upper layer is a layer of the first type and therefore has a refractive index which is higher than the index refraction of the upper layer; and in which the stack of layers comprises at least one additional layer which is arranged under the two upper layers in the stack of layers and which is a layer of the third type and therefore has a refractive index which is lower than the refractive indices of the two layers higher.

According to a preferred embodiment of the invention, the upper layer or layer of the second type is an oxide layer. This is advantageous since some oxides such as those listed below combine high abrasion resistance with a medium to high refractive index.

On the other hand, the layer with the highest refractive index can be made of the same material as the substrate, for example in ZnS. This can be an advantage when using another layer material for the first layer, which has good adhesion properties on the substrate and can therefore potentially be combined very well with the respective layer material. .

In order to be usable for a plurality of wavelength ranges of the electromagnetic spectrum, the substrate and the stack of layers are at least partially transparent in the infrared and visible spectral range. In particular, the wavelength range from 450 nm to 650 nm is considered to be the visible spectral range. According to one of embodiments of the invention, the interference layer system can now be designed so that the substrate and the stack of layers are at least partially transparent in at least one, preferably in several and especially in all of the following wavelength ranges:

- in the range from 450 nm to 650 nm;

- at one or more wavelengths in the range from 1000 nm to 1600 nm;

- in the range from 3500 nm to 5000 nm;

- In the range from 7,500 nm to 12,000 nm.

Typically, more than three layers of the stack of layers are useful for obtaining good anti-reflection properties in a plurality of wavelength ranges. In this case, it is preferable to form the stack of layers as a system of alternating layers with alternating layers of the first and third types and to provide a layer of the second type as the last upper layer. A layer of the second type is deposited to finish, so that the second upper layer is a layer of the first type with a high refractive index, as envisaged according to the invention. The second upper layer may be a layer of the third type if its thickness is preferably less than 300 nm, in particular less than 100 nm and particularly advantageously less than nm. Alternatively, layers of the third type can also be replaced by a layer of the second type, so that the replacement layer of the second type is surrounded on both sides by a respective layer of the first type. This can be advantageous because the material of the second type is harder than the material of the third type according to the invention, and since the scratch resistance depends not only on the properties of a surface but also on the stability of the underlying materials. and layers supporting the surface layer. The reverse phenomenon is more commonly known as the "chocolate coated marshmallow" effect, where an inherently rather hard surface (chocolate) can break and sink into a softer underlying material (sugar foam). To counter this effect, where the two upper layers of the second and first type break in the third upper layer of the third material, it is therefore advantageous that not only the upper layer is made of a material of the second type, but also the third upper layer and possibly also the fifth upper layer. For reasons of simplicity, the layers made of materials of the second type are even made of the same material, and such a layer system can be deposited using only three materials.

In general, in this case it will be advantageous for the stack of layers to have a plurality of layers of the first type and a plurality of layers of the third type (at least two layers in each case) and a single layer of the second type, which ends the stack of layers and forms the uppermost layer of the stack of layers.

According to another preferred embodiment of the invention, the substrate of the optical component consists of zinc sulfide. This substrate also has the particularity of being transparent to the wavelengths indicated above.

If the layer of the second type and therefore the upper layer is an oxide layer, it preferably comprises a material chosen from the group comprising hafnium oxide (HfO ₂ ), scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ) , titanium oxide (TiO ₂ ), aluminum oxide (A1 ₂ O ₃ ) and cerium oxide (CeO ₂ ) and mixed oxides of these oxides. The reason for this choice is that the materials or mixtures cited have a medium to high refractive index. The refractive index of these materials is in the range of 1.7 to 2.2.

On the other hand, according to a preferred embodiment of the optical component, the additional layer is a layer of fluoride. Thanks to the refractive indices of the fluorides used, the anti-reflective behavior of the coating of the optical component is further improved. In addition, many fluorides are transparent over much of the wavelength ranges shown.

In this case, the additional layer comprises a fluoride chosen from the group comprising barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride ( LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride (YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (A1F ₃ ), dysprosium fluoride (DyF ₃ ) and yttrium fluoride (YF ₃ ). These materials have refractive indices between 1.3 and 1.9.

The second upper layer consists of a material having a higher refractive index than that of the material of the upper layer and can be chosen from the group of chalcogenides, in particular from the group of oxides, sulfides or selenides (which, with tellurides, are called chalcogenides) and which is transparent in the respective ranges of the wavelengths, like the sulfide ZnS. The second upper layer may be a layer of the third type if its thickness is preferably less than 300 nm, in particular less than 100 nm and preferably less than 20 nm.

On the other hand, it is possible to provide an embodiment of the coating according to which a material is chosen for the first layer, which has particularly good adhesive properties or at least better adhesive properties on the substrate than the material. of the third type. The main purpose of this layer is to promote adhesion between the substrate and the coating. Thus, the layer fulfills a chemical-mechanical and not an optical function. To this end, this first layer may have a thickness of only a few nanometers. For example, the thickness of the layer can be between 1 nm and 15 nm. Thus, in certain applications with respective transmission requirements, it is even possible to use layer materials which transmit less well in the relevant wavelength ranges than the materials of the first, second and third types mentioned above. For example, aluminum oxide (A1 ₂ O ₃ ) is known to be such an adhesion promoter.

In a specific embodiment of this version with better adhesion of the layer, the adhesion promoting layer consists of a material of the second type, for example HfO ₂ . Since in this case the material can be used as an optical layer material, thanks to its transparency properties, the thickness of the adhesion-promoting layer can in turn be large enough to fulfill a function in the context of optical design.

There are different techniques that can be used to coat the optical component according to the invention. The upper layer can in particular be applied by a method chosen from the group comprising ion plating, ion implantation, ion assistance / advanced plasma, magnetron sputtering, ion beam sputtering, cathodic arc deposition and deposition by atomic layer. Ionic or plasma assistance is particularly advantageous for increasing the density, hardness and compressive stress of the upper layer in order to make it more resistant to abrasion.

In addition, the upper layer of the coating of the optical component according to the invention can be deposited by a process different from the other layers of the stack of layers. If more than one layer is made of the material of the last layer, it is even possible to deposit the last layer with one process and the other or other layers made of the same material according to a different process. This is particularly advantageous if a method used to increase the density, hardness or compressive stress of the top layer is incompatible with another layer material.

According to a particular embodiment of the invention, the stack of layers, with the exception of the upper layer which itself consists of two or more materials, is deposited by conventional electron beam evaporation, and for the last layer, an ionic or plasma process, such as ion plating, ion assist or advanced plasma, is additionally activated.

It may be advantageous to begin first depositing the upper layer without the additional ionic or plasma process, in order to protect, with the first nanometers of material, the material of the second upper layer underlying the process ionic or plasma. Therefore, the top layer will be subdivided into two sublayers of the same material which have a similar but not identical refractive index. Typically, the part deposited using in addition the ionic or plasma method will have a slightly higher refractive index than the part which was deposited without the additional method.

According to another embodiment, this protective layer, which protects the old second upper layer against the ionic or plasma process, can be made of another material. This layer fulfills a mechanical or radio technical function but not an optical one. For this purpose, the thickness of this first layer can be only a few nanometers. Thus, in certain applications with respective transmission requirements, it is even possible to use layer materials which transmit less well in the relevant wavelength ranges than the materials of the first, second and third types mentioned above. . For example aluminum oxide (A1 ₂ O ₃ ) can be used for such a protective layer, but also materials of the third type.

The stack of layers may comprise a succession of alternating layers which comprises at least one other layer made of the same material as one of the three upper layers.

The lower layer 9 can be a layer of the third type of layer 5 having the lowest refractive index.

According to one embodiment, the stack of layers has a number between seven and thirty layers in total, with four respective layers of the type of the additional layer alternating with those of the type of the second upper layer, or four layers respective of the third type alternating with four layers of the first type. In addition, the top layer is added as a final layer which, at the same time, seals the stack of layers from the environment. It has been found that with this embodiment, the anti-reflective properties are particularly good.

According to the invention, the optical component is used in a single spectral domain or in visible and infrared multispectral domains of the electromagnetic spectrum.

In another embodiment, so-called "needle" layers are interposed in at least one layer which is generally relatively thick. The needle layers are layers having a thickness of a few nanometers, preferably from 2 nm to around 50 nm. The lower limit of the thickness of the needle layers is generally imposed by the coating technology. In the case of electron-vapor deposition, layers with a thickness of less than 5 to 10 nm are generally not contiguous or are too heterogeneous, depending on the material of the layer, to be used in the application . However, certain chemical vapor deposition procedures, such as atomic layer deposition (ALD), make it possible to obtain useful layers of 2 or 3 nm, for example.

The needle layers have several advantages. For example, they stop the growth of crystals and limit the periphery of the grains. The layers are statistically more amorphous and have fewer defects and less light scattering. Another advantage is that the layer stress can be reduced and compensated for. The substrate has less deformation induced by the coating (distortion of the reflected wavefront), and the risk of delamination of the layers, either at the interface with the substrate, or between the coating layers, is reduced. Often this is even visually advantageous, and the spectral performance of a coating can be increased without significantly increasing the total thickness of the stack of layers of the coating. This has advantages in terms of time and therefore cost of applying the coating. Needle layers are known to those skilled in the art of designing optical coatings. They are particularly useful in the coatings of the present disclosure, as relatively thick layers must be used due to the fact that the coating is designed to be optically transparent over a very wide range of wavelengths, up to far infrared.

Here is an example of a coating according to the invention which comprises needle layers: the coating materials used for a coating on a zinc sulfide substrate include zinc sulfide (ZnS) having a refractive index of 2.24, yttrium fluoride (YF ₃ ) having a refractive index of 1.47 and hafnium oxide (HfO ₂ ) having a refractive index of 2.01, for a wavelength of 1000 nm in each case. The coating is obtained by electron beam evaporation. The upper layer of hafnium oxide is divided into two parts with regard to the coating process: the first 10 nanometers are deposited by normal electron beam evaporation - the rest of the layer is deposited using a advanced plasma source (APS). The layer thicknesses are as follows: substrate (ZnS), (l ^CE) 10 nm HfO2, (2 ^nd) 25 nm YL3, (3 ^rd) 25 nm ZnS, ^(4th) 225.8 nm YL3, (5 ^th) 10 nm ZnS, (6 ^th ) 250 nm YL3, (7 ^th ) 10 nm ZnS, (8 ^th ) 250 nm YL3, (9 ^th ) 10 nm ZnS, (10 ^è “) 250 nm YL3, (1 l ^è ” ^e ) 10 nm ZnS, (12—) 150 nm YL3, (13 ^th ) 10 nm ZnS, (14 ^th ) 50 nm YL3, (15 ^th ) 60 nm ZnS, (16 ^th ) 65 nm HfO ₂ , air. This example represents an anti-reflective coating for the visible spectral range and for the far infrared from 8 to 11 μm. Such a structure can be interpreted in two ways: (1) thick layers of a material alternate with thin layers of another material; or (2) a very thick part with a low refractive index is interrupted by very thin needle layers with a high refractive index: a thick part with a low refractive index, comprising 225.8 nm + 250 nm + 250 nm + 250 nm + 150 nm + 50 nm = 1,175.8 nm of YL ₃ , is interrupted by 5 needle layers each consisting of 10 nm ZnS. For light, in particular long wavelength radiation in the far infrared (LIR), the length of the optical path and therefore the phase change in the needle layer is negligible. Interaction with matter is mainly determined by the reflectivity at the two interfaces.

Thus, more generally and without being limited to the example above, the embodiment with the needle layers represents a system of alternating layers forming part of the coating, in which layers of two types alternate, the layers of one type being thicker than those of the other type. This system of alternating layers preferably comprises at least four successive layers in total. Preferably, the layers of one type are always at least a factor of ten thicker than the layers of the other type. In addition, the thin layers may in particular be of the first type (that is to say with a high refractive index), and the thick layers may be of the third type (that is to say with a low refractive index) ). In addition, depending on the thickness of the needle layers as indicated above, the thinner layers preferably have a layer thickness of between 2 nm and 50 nm.

A coating according to the invention can include any desired number of portions having a thickness of 100 nm or more, which are interrupted by needle layers: no portion, or else a number between one portion and all the portions. Any portion of a material having a thickness of 100 nm or more can be interrupted by the complete absence of a needle layer or by one or more layers. Different portions having a thickness of 100 nm can be interrupted by different numbers of needle layers. It is possible to interrupt portions made of a material and having a thickness of 100 nm or more, by needle layers of one or more other materials, and also to interrupt portions made of different materials and having a thickness 100 nm, by needle layers of one or more other materials. Some or all of the needle layers can be made of a third material different from the two materials that mainly make up the layer system, as layers with a high and low refractive index. If a liner design that already contains needle layers is communicated for optimization in optimization software, or if the optimization software receives a liner design that already has needle layers, for optimization , it may happen that an optimized design includes needle layers which not only make it advantageous in terms of mechanics, but that the design also has a quality in terms of spectral or optical behavior which is superior to a comparable optimized design without layers needles.

According to a particular embodiment, it is advantageous to protect the layers already deposited with needle layers made of a third material, before the process of depositing the next layer which has a relevant optical thickness. This is for example the case if the plasma assistance processes for a layer to be deposited damaged an already deposited layer and broke, for example, covalent bonds or dissolved the atoms of a species from which the underlying layer is made and would modify the material on the surface, so that it would adopt an unfavorable composition in terms of stoichiometry, which would have the consequence that it would exhibit, for example, a higher absorbency. In this case, it is advantageous to deposit a needle layer only on a layer of the material which is sensitive to the deposition process of the other material. Furthermore, in another case, it is possible that, although two materials can be used together with optical advantages for a design, the two materials are not compatible with each other for other reasons. Examples of incompatibilities include, for example, insufficient adhesion of the layers or chemical alteration of a layer material caused by the reaction of one of its atomic species with a species of the other material at the interface, forming thus a different material, optically unfavorable. Such a reaction can occur either immediately during the coating process, or during a subsequent annealing process (thermal annealing), or later, through an accelerated or additional aging or degradation process. In the example above, a needle layer was deposited directly on the substrate, as a first layer, to be effective as a promoter of adhesion between the substrate and the rest of the coating. It is particularly judicious to protect by a needle layer the penultimate thick layer vis-à-vis a plasma process which can be used for the last layer, in order to confer on this layer, and therefore on the whole coating, a particularly high resistance to abrasion.

According to another embodiment, so-called “nanostratified” structures can be used as individual layers. The references describing the "nanostratified", that is to say very thin layers with a thickness ranging for example from 2 to 10 nm, include, among others, J. Meyer, et al: "Al ₂ O ₃ / ZrO ₂ Nanolaminates as Ultrahigh Gas-Diffusion Barriers - A Strategy for Reliable Encapsulation of Organic Electronics ”, in: Advanced Mater. 2009, 21 1845-1849, WileyVCH Weinheim editions, 2009; or J. Meyer: "The origin of low water vapor transmission rates through Al ₂ O ₃ / ZrO ₂ nanolaminate gas-diffusion barriers grown by atomic layer deposition", in: Applied Physics Letters 96, 243308 (2010), American Institute of Physics , 2010.

The nanostratified are layers made up of a multitude of very thin layers, generally formed from two alternating materials. For example, a nanostructured layer can be composed of A1 ₂ O ₃ and HfO ₂ , or of Al ₂ O ₃ and Ta ₂ O ₅ . It is of course possible to compose such nanostratified from more than two materials. The individual layers are generally a few nanometers thick. Such a nanostratifier acts optically as a thick layer having an average refractive index and can therefore be integrated into a multilayer interference coating with other thicker layers made of one or more other materials. These nanostratified are generally used because of their advantageous mechanical properties. A nanostructure could be interpreted as a set of layers composed exclusively of needle layers.

The nanostratified reach their property due to the large number of interfaces and very thin layers in which the overall properties are partially negligible. The parameters which have a significant influence on the properties of the nanostratified materials and which do not exist for the monolithic layers include, for example, what is called the "service factor", that is to say the ratio of thicknesses of the different needle layers to each other. Typical examples are 3 nm of Al ₂ O ₃ and Ta ₂ O ₅ , respectively, or 3 nm of Al ₂ O ₃ alternating with 10 nm of Ta ₂ O ₅ . Such layer thicknesses cannot be produced homogeneously by conventional methods of electron vapor deposition. However, there are other methods, such as atomic layer deposition (ALD), which are used in the cited publications. It is even possible to grow other layers of the coating by ALD. The examples described use ZnS and YL ₃ . The two materials can also be deposited by ALD: JRBakke, et al: "Atomic layer deposition of ZnS via in situ production of H ₂ S", in Thin Solid Lilms, volume 518, number 19, 2010, 5400-5408; and Tero Pilvi, et al: "ALD of YL ₃ Thin Lilms from TiL ₄ and Y (thd) 3 Precursors" in Chemical Vapor deposition, volume 15, number 1-3, 2009, 27-32.

In a coating according to the invention, one or more of the layers can be produced in the form of nanostratified. The nanostratified can be high index layers and low index layers, as well as medium index layers. It may in particular be advantageous to produce the last layer in the form of a nanostratified consisting of an oxide and a fluoride. Thus, the advantage of the relatively higher hardness of the oxide compared to fluoride is combined with the advantage that such a nanostructured has a lower optically relevant average refractive index than hard oxide. For the optical quality of a coating design which should have low reflectivity, it is preferable that the last layer has as low a refractive index as possible. In this regard, it is also possible to optimize the service factor, so that the nanostratified is composed of more fluoride than oxide and that the refractive index is thus lower than that of a nanostratified. composed of 50% fluoride and 50% oxide, while also having a hardness or abrasion resistance significantly higher than a pure fluoride.

More generally, without being limited to specific examples, it is therefore envisaged, in accordance with an embodiment of the invention, that at least one of the layers of the coating is a nanostratified consisting of a multitude of layers d 'a thickness between 2 nm and 10 nm, and that these layers consist of at least two alternating materials.

According to other embodiments, the upper layer of the coating is a nanostratified, as mentioned above. In particular, it may include a system of alternating layers of fluoride and oxide, as explained above.

Furthermore, it is known from patent application publications CH 709 524 A2 ("Harte Anti-Reflex-Beschichtungen sowie deren Herstellung und Verwendung" ("Hard anti-reflective coatings as well as their manufacture and use")), and DE 10 2016 125 689.7 ("Substrate umfassend Anti-Reflex-Beschichtungs-system mit Hartstoffbeschichtung sowie Verfahren zu dessen Herstellung" ("Substrate comprising an anti-reflective coating system with hard-material coating and process for its manufacture")) that higher abrasion resistance of a multilayer coating can also be obtained if, although the upper layer is not changed, the lower layers are made substantially harder or more stable. This phenomenon can now also be applied to the coating according to the invention, by producing a layer which is arranged under the upper layer in the form of nanostructure in order to have greater hardness. For example, the last layer that includes ZnS can be composed of a nanostratified and an oxide and can therefore offer greater stability by supporting the final layer with a low refractive index.

The invention will now be described in more detail with reference to the accompanying drawings in which identical references denote identical elements.

Brief description of the drawings In the drawings:

[Fig-1] is a schematic view of the stack of layers of the optical component according to the invention;

[Fig.2] is a transmittance graph of a 4-band anti-reflective coating on a ZnS substrate 4 mm thick;

[Fig.3] is a schematic view of the stack of layers of the optical component of the invention according to Figure 1, provided with an additional layer promoting adhesion;

[Fig.4] is a schematic view of the stack of layers of the optical component of the invention according to Figure 1, wherein the upper layer is divided into two sublayers;

[Fig.5] is a schematic view of the stack of layers of the optical component of the invention according to Figure 1, provided with an additional protective layer;

[Fig.6] is a schematic view of the stack of layers of the optical component of the invention according to Figure 1, with needle layers or thin intermediate layers; and [fig.7] is a schematic view of the stack of layers of the optical component of the invention according to Figure 1, provided with a nanostructure.

Without limiting itself to the structure of the layers illustrated, FIG. 1 shows a schematic sectional view of the succession of layers of the stack of layers 2 of an optical component 10, which stack of layers 2 serves as an anti-reflective coating .

An optical component 10 with an anti-reflective coating according to the invention is produced by a method according to which a substrate 1 is provided with a stack of layers 2, comprising a plurality of successive layers of different materials and with refractive indices different, which constitutes an anti-reflective coating in which the layers of the stack of layers 2 are deposited successively from at least three different materials or combinations of materials, so that the stack of layers produced by the successive deposition comprises at least a layer of a first type, of a second type and of a third type, with at least three different refractive indices, a layer of the first type having a refractive index greater than that of a layer of the second type, and a layer of the third type having a refractive index lower than that of a layer of the second type; and in which an upper layer and a second upper layer are provided, the upper layer 7 being a layer of the second type 3, and the second upper layer being a layer of the first type 4 and therefore having a refractive index which is greater than 1 'refractive index of the upper layer; and in which the stack of layers 2 comprises at least one other layer which is arranged under the two upper layers in the stack of layers 2 and which is a layer of the third type 5 and therefore has a refractive index which is lower than the indices of refraction of the two upper layers.

The substrate 1 of the illustrated example is provided with a stack of layers 2 which here consists of a total of nine successive layers made of different materials and having different refractive indices. The layers of the layer stack 2 are formed from at least three different materials or combinations of materials, so that the layer stack comprises at least one layer of each of the first, second and third types. The types of layers differ in their refractive indices, so the stack contains layers with at least three different refractive indices. In this case, a layer of the first type 4 has a higher refractive index than a layer of the second type 3, and a layer of the third type 5 has a lower refractive index than a layer of the second type 3. The upper layer 7 of the stack of layers 2 is in contact with the environment and is therefore exposed to the influences of the ambient environment and must therefore be made of a material as resistant as possible to abrasion.

The upper layer 7 is a layer of the second type 3, and the second upper layer is a layer of the first type 4 and therefore has a refractive index which is even higher than the refractive index of the upper layer 3 The stack of layers 2 comprises at least one additional layer which is placed under the two upper layers of the stack of layers 2 and which is a layer of the third type 5 and therefore has a refractive index lower than the refractive indices of the two upper layers of the first and second types 4, 3. Below the succession consisting of the upper layer 3, the second upper layer 4 and the additional layer 5, there are provided alternating layers which are made of the same material as the second upper layer 4 and the additional layer 5.

In the embodiment of Figure 1, there are four layers of each type of the second upper layer 4 and the additional layer 5, alternating with each other under the upper layer 3, so that the stack of layers illustrated comprises a total of nine layers if the upper layer 3 is taken into account, which corresponds to a preferred embodiment of the antireflection coating, since the antireflection behavior is particularly good in this configuration. The alternating layers of the first and third types 4, 5 form a system of alternating layers. The stack of layers is then completed by a single layer of the second type, as the upper layer. Since the refractive index of the upper layer is lower than the refractive index of the second upper layer, on the one hand, an anti-reflection effect is obtained, despite the higher refractive indices compared to the layers of the third. type, and, on the other hand, high mechanical strength.

The substrate 1 may in particular consist of zinc sulfide. According to one embodiment, the second upper layer 4 is made of the same material as the substrate 1, that is to say in particular of zinc sulfide, ZnS.

In particular, one of the following oxides is suitable as a material for the upper layer 3 or the layer of the second type: hafnium oxide (HfO ₂ ), scandium oxide (Sc ₂ O ₃ ), l zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ), titanium (TiO ₂ ), aluminum oxide (A1 ₂ O ₃ ) and cerium oxide (CeO ₂ ). The reason for this choice is the combination of the refractive indices and the hardness of these substances. An increased hardness of the upper layer 3 is further obtained by applying the upper layer 3 with special techniques to make it particularly hard. The following techniques can be used for this purpose: ion plating, ion implantation, ion assistance / advanced plasma, magnetron sputtering, ion beam sputtering, cathode arc deposition and atomic layer deposition. It is not necessary to use the same technique to apply all the layers in the stack of layers 2. Different techniques can be combined with one another. For example, according to one embodiment, all the layers, with the exception of the upper layer 3, can be thermally deposited by vapor deposition, while the upper layer 3 is applied by spraying. A change in the coating technique remains economical insofar as it must be carried out only for the top layer.

In particular, one of the following fluorides is suitable as a material for one or more layers of the third type 5: barium fluoride (BaE ₂ ), calcium fluoride (CaE ₂ ), cerium fluoride (CeE ₃ ), lanthanum fluoride (LaE ₃ ), neodymium fluoride (NdE ₃ ), ytterbium fluoride (YbE ₃ ), magnesium fluoride (MgE ₂ ), aluminum fluoride (A1E ₃ ), dysprosium fluoride (DyE ₃ ) and yttrium fluoride (YE ₃ ). The material of the layer of the third type 5 is chosen so that the refractive index of the different layers increases from the additional layer 5 to the upper layer 3, passing through the second upper layer 4.

According to an example, the upper layer is a layer of the ^2nd type and therefore a layer of HfO2. This layer is deposited on a layer of ZnS which is a layer of the ^1st type. This layer is followed by a layer of the 3 ^rd type or one or more other optional layers followed by the layer of the ^3rd type, layer 3 ^rd type being a YF3 layer. This layer may be in contact with the substrate or, alternatively, one or more other optional layers may be interposed between the substrate and the layer of the ^3rd kind. This embodiment is particularly suitable for a substrate of zinc selenide (ZnSe). However, a ZnS substrate is also suitable. In summary, the layer sequence according to this embodiment is as follows: HfO2 ^(2nd type) / ZnS ⁽¹ type) / optional layers / YF 3 (3 ^rd type) / optional layers / ZnSe substrate.

As an alternative to HfO ₂ , the layer or layers of the second type can be layers of Sc ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , A1 ₂ O ₃ , CeO ₂ . On the other hand, alternative materials to YF3 for layer 3 ^rd type are BaF _2, CaF _2, CeF _2, LaF _3, NdF _3, YbF _3, MgF _2, A1F _3, DyF _3, DyF _3.

The overall structure consisting of the substrate 1 and the stack of layers 2 is at least partially transparent in the spectral ranges of infrared and visible, at wavelengths between 450 nm and 650 nm, at one or several wavelengths between 1000 nm and 1600 nm, at wavelengths between 3500 nm and 5000 nm, and in the far infrared at wavelengths ranging from 8 pm to 12 pm, this which allows for example to use it as a window for cameras which are sensitive in the wavelength ranges mentioned.

The invention is particularly suitable for infrared optics, including lens systems. Such infrared optics can then be combined with a plurality of sensors which are sensitive in the spectral ranges of visible and infrared. This is for example the case with range finders or thermal cameras. A preferred application is to be used as a cover window for an infrared camera, for example in an airplane, a tank, a motor vehicle or a drone.

FIG. 2 represents a graph of the transmittance plotted as a function of the wavelength of an anti-reflective coating of a ZnS substrate with a thickness of between 1 and 4 mm, which is at least partially transparent for four frequency ranges, in which a logarithmic scale has been selected for the wavelength. The graph in Figure 2 shows the transmittance profile as a percentage of the incident radiation.

The transmittance profile of an uncoated substrate is represented by curve 22 which, at a wavelength of approximately 380 nm, rises almost vertically with an increasing wavelength up to 65% , and at a wavelength of about 1000 nm, at 74%, it becomes a horizontal section.

The transmittance of a substrate coated on both sides, in accordance with the invention, is represented by the curve 21 which follows a specification of transmittance in four sections 21a, 21b, 21c, 21d. In section 21a between 420 nm and 720 nm, which is the range of visible wavelengths, the transmittance is everywhere approximately 20% greater than that of curve 22 of an uncoated substrate. From 1,530 to 1,550 nm, which is the wavelength of the so-called “eye-safe” LIDARs or rangefinders, the transmittance profile has another section 21b which has a peak clearly greater than 90% at this length of d wave and is therefore also about 20% higher than the transmittance of the uncoated substrate. The transmittance of a coated substrate according to the invention has another section of high transmittance, which greatly increases at a wavelength of approximately 3000 nm. At a wavelength of around 13,000 nm, the transmittance decreases sharply. In general, two wavelength ranges are used in this field of technical applications, firstly the range 21c ranging from 3500 nm to 5000 nm for the detection of objects at high temperature, such as motors with reaction or internal combustion engines, and then the range 21d, from 7,500 nm to 11,500 nm, to detect body temperature. In these two ranges, the transmittance profile 21 of the coated substrate also has a transmittance approximately 20% greater than the curve 22 of the uncoated substrate.

It is therefore an anti-reflective coating with 4 bands. It is transparent and has an anti-reflective effect in the wavelength ranges of the visible spectral range, for a rangefinder called "harmless to the eyes", as well as for the thermal radiation of motors and living bodies.

The example of a coating according to the invention consists of the three layer materials YE ₃ , ZnS and HfO ₂ . In the example presented, the three layers of materials have the following refractive indices:

[Tablesl]

Material Coating technology Refractive index at 1000 nm ye ₃ Electron beam 1.49 ZnS Electron beam 2.28 HfO ₂ Electron beam 1.90 HfO ₂ Ion plating 2.11

The last two layers of this example are each made of HfO ₂ . However, the first half is deposited by a standard vapor deposition process by electron beam (electron beam). The second half is deposited by ion plating. In this way, the last non-oxidizing layer is protected, by the first sublayer of HfO ₂ , from the ion plating process which would damage the underlying non-oxidizing layer and degrade its power of transmission or absorption in the sense of l 'invention. The structure of the layers is as follows: substrate, 20.1 nm YL ₃ ,

36.1 nm ZnS, 60.3 nm YL ₃ , 25.8 nm ZnS, 42.7 nm YL ₃ , 243.6 nm ZnS, 168.5 nm YL ₃ ,

89.2 nm ZnS, 170.2 nm YL ₃ , 46.1 nm ZnS, 35.6 nm HfO ₂ (electron beam), 35.6 nm HfO ₂ (ion plating), air. The result of a two-sided coating with this design, on a 10 mm thick ZnS substrate, is the measured transmittance spectrum 21.

FIG. 3 represents an embodiment in which an additional layer 6 promoting adhesion is applied to the substrate 1 in order to improve the adhesion of the stack of layers 2 on the substrate 1. This layer 6 promoting the adhesion is generally characterized by the fact that it adheres better to the substrate 1 than a layer 5 of the third type. According to a first embodiment of the invention, the layer 6 promoting adhesion can be kept thin enough not to influence, or only marginally, the reflection properties of the stack of layers, in optical terms. Preferably, the thickness of the layer is at least 1 nm and / or preferably less than 10 nm in the present case. With a thin layer, it is more generally possible to use a material having a higher absorption coefficient in the visible and / or infrared spectral range than the materials of the first, second and third types, because due due to the small thickness of the layer, the total transmittance would not be reduced significantly. Aluminum oxide A1 ₂ O ₃ , which provides high adhesion to many substrate materials, is a suitable material for the adhesion promoting layer.

According to yet another embodiment of the invention, the layer 6 promoting adhesion can at the same time be an optically active constituent of the stack of layers 2, which contributes to the anti-reflective effect. To this end, the layer 6 promoting adhesion can in particular be a layer of the second type.

In the embodiment according to Figure 4, the upper layer 7 is divided into a second sublayer 11 and a first sublayer 12, the first sublayer 12 defining the surface of the stack of layers 2. The second sublayer 11 is applied without an ionic or plasma assistance method, and for the deposition of the first sublayer 12 such an assistance method is used. In this way, it is avoided that the high-energy ions do not chemically or physically damage the underlying layer 4 of the first type, during the ion-assisted deposition process. On the other hand, the ionic assistance makes it possible to obtain a dense layer structure of the first sublayer 12. Thus, although the two sublayers 11 and 12 are made of the same material, they are different in terms of density. Typically, the first sub-layer 12 will have a higher density and therefore a higher refractive index. The ionic assistance makes it possible to obtain a dense and resistant surface.

In the embodiment according to Figure 5, an additional protective layer 13 is applied under the upper layer 7 or before it, in order to protect the material of the layer 4 during the deposition of the upper layer 7 against the ionic or plasma process. Consequently, it is generally provided in this embodiment that the protective layer is deposited before the upper layer 7, and that the upper layer 7 is deposited on the protective layer and in contact with the latter.

In the embodiment according to Figure 6, the optical component 10 comprises a system of alternating layers in which the layers 4 made of the material of the first type alternate with the layers 5 made of the material of the third type. The layers 4 have a thickness which is at least a factor of 10 greater than the thickness of the layers 5. The latter layers, which are in the form of very thin intermediate layers, are also called "needle layers".

In the embodiment according to FIG. 7, one of the two layers 4 is produced in the form of what is called a “nanostratified” 50. This layer comprises several successive thin layers, with a thickness between 2 nm and 10 nm.

The coating according to the invention was subjected to two standardized tests to check its resistance to scratches or abrasion. The first standardized test was the Bayer test according to ASTM L735-11, TABER. The abrasive medium used in this case was silica sand which has the following properties:

[Tables2]

Ranking 5/9 Round 0,6+ Sphericity 0,6+ Hardness 7.0 P. S. 2.65 Loss on calcination 0.1 Fusion bridge 2,800 ° / 3,100 ° Color brown / white PH 6.9 7.0

The typical chemical composition of the silica sand used is as follows, in percentage by weight:

[Tables3]

SiO ₂ 99.48% by weight Fe ₂ O ₃ 0.06% by weight A1 ₂ O ₃ 0.21% by weight MgO <0.01% by weight

This silica sand is commercially available from Rimer Silica, Texas, United States.

Another relevant test for such applications and coatings is the so-called "wiper test", sometimes called washability test, according to standard TS1888. The coated sample is mounted in a holder, and the coated outer surface is subjected for 5 minutes to 1000 wiping cycles per hour (2000 passages per hour) by a standard automotive wiper lip, with a load 20 grams per centimeter and with the addition of a mixture of sand and water (1 cm ³ of sand according to DEF STAN 07-55 type C in 10 milliliters of water).

At the end of the test, the sample must not show any visible sign of scratching during visual inspection.

In this test, a standard coating with a fluoride as the upper final layer was reduced in its layer thickness by 70 nm on average (macroscopically), while the reduction in the thickness of the coating conforms to the invention was only 12 nm on average (macroscopically). Both coatings had the same spectral specifications. To analyze these reduced layer thicknesses, a reverse engineering operation was carried out on the design of the optical layer of the reflection spectra measured before and after the abrasion.

Another standardized test to check the abrasion resistance was the wiper test according to standard TS1888, with dirty water. In this case, the wiper exerts a pressure of 22 N and performs 100 movements per minute over an angular range of 60 degrees. The percentage of weathering in the haze is measured at appropriate intervals, in accordance with ASTM D1003. When the average value of the haze of the average field of vision reaches 5%, this value is generally considered as the end of the lifespan.

Other possibilities of checking the abrasion resistance consist in a modified Bayer test, using corundum sand, and in sand and dust abrasion according to the MIL-STD-810G% 10.5 method. A gum abrasion test according to DIN ISO 9211-4-01-03 can also be carried out.

The measurement of the abrasion resistance is carried out so that at least one of the following parameters is measured before and after the execution of at least one of the test methods described:

- quantity of surface defects according to ISO10110;

- size of surface defects according to ISO10110;

- scattering of light, measured on the basis of the value of dry mist;

- Reflection in a range of predefined wavelengths;

[0111] - transmittance in a predefined wavelength range; or [0112] - sharpness of the image (DOI) transmitted by the component.

When an optical component according to the invention is compared to a component having the same substrate material and a coating comparable from the point of view of its optical behavior, but in which the upper layer consists of a fluoride, a significant improvement in abrasion resistance is obtained for a component according to the invention. Compared to an optical component which has an upper fluoride layer as indicated above, it appears that, although the aforementioned parameters (quantity and size of surface defects according to ISOIOHO, etc.) also deteriorate for an optical component according to the invention, this deterioration is at least 20% less than that of the optical component having the upper fluoride layer.

It will be clear to those skilled in the art that the invention is not limited to the embodiments illustrated by way of examples in the figures, but that it can rather be modified within the scope of the subject of claims. The characteristics of the various exemplary embodiments can in particular be combined with one another.

[0115] List of references [0116] 1 Substrate [0117] 2 Stacking of layers [0118] 3 Layer of second type [0119] 4 Layer of first type [0120] 5 Layer of third type [0121] 6 Additional layer favoring the adhesion [0122] 7 Upper layer [0123] 9 Lower layer [0124] 10 Optical component [0125] 11 Second underlay of 7 [0126] 12 First underlay of 7 [0127] 13 Additional protective layer [0128 ] 21a, b, c, d Transmittance profile with anti-reflective coating [0129] 22 Transmittance profile without anti-reflective coating [0130] 50 Nanostratified

Claims (1)

claims [Claim 1] Optical component (10), comprising a substrate (1) provided with a stack of layers (2) which comprises a plurality of successive layers of different materials and with different refractive indices, which defines an anti-reflective coating, characterized in that the layers of the stack of layers (2) consist of at least three different materials or combinations of materials, so that the stack of layers comprises at least one layer of a first type, of a second type and of a third type, with at least three different refractive indices, where a layer of the first type has a higher refractive index than a layer of the second type, and a layer of the third type has a lower refractive index than a layer of the second type; and in which an upper layer and a second upper layer are provided, knowing that the upper layer (7) is a layer of the second type (3), and the second upper layer is a layer of the first type (4) and therefore has a refractive index which is higher than the refractive index of the upper layer; and in which the stack of layers (2) comprises at least one additional layer which is arranged under the two upper layers of the stack of layers (2) and which is a layer of the third type (5) and thus has an index of refraction which is lower than the refractive indices of the two upper layers. [Claim 2] Optical component according to the preceding claim, characterized in that it comprises a layer with a low refractive index with a thickness between 2 nm and 50 nm, which is interposed between the last two layers. [Claim 3] Optical component (10) according to any one of the preceding claims, characterized in that the upper layer is an oxide layer. [Claim 4] Optical component (10) according to any one of the preceding claims, characterized in that the layer (4) having the highest refractive index is produced from the same material as the substrate (1). [Claim 5] Optical component (10) according to any one of the preceding claims, characterized in that the stack of layers (2) is produced in the form of a system of alternating layers comprising alternating layers of the first and third types and a layer of the second type as an upper layer. [Claim 6] Optical component (10) according to any one of the preceding claims, characterized in that the stack of layers (2) comprises a plurality of layers of the first type and a plurality of layers of the third type (4, 5), and a single layer of the second type (3) which forms the upper layer of the stack of layers (2). [Claim 7] Optical component according to any one of the preceding claims, characterized in that the stack of layers (2) comprises an adhesion-promoting layer (6) which has better adhesion to the substrate (1) than a layer of the third type . [Claim 8] Optical component according to claim 6, characterized in that the adhesion promoting layer (6) consists of a material chosen from the group comprising aluminum oxide and hafnium oxide, or is a layer of the second type. [Claim 9] Optical component according to any one of the preceding claims, characterized in that the upper layer (7) comprises a first sublayer (12) and a second sublayer (11) of the same material, but with a different refractive index . [Claim 10] Optical component according to any one of the preceding claims, characterized in that it comprises a protective layer (13) deposited before the upper layer (7), the upper layer (7) being deposited on the protective layer (13) and in contact with it, the protective layer (13) being a layer of the third type and having a layer thickness less than 300 nm, preferably less than 200 nm and particularly advantageously less than 20 nm. [Claim 11] Optical component according to any one of the preceding claims, characterized in that the coating comprises a system of alternating layers in which layers of two types alternate, in which the layers of one type are thicker than the layers of the other type, in which at least one of the following characteristics is applicable: the system of alternating layers preferably comprises a total of at least four successive layers; - the layers of one type are at least ten times thicker than the layers of the other type; - the thin layers are layers of the third type, and the thick layers are layers of the first type; - the thin layers have a thickness of between 2 nm and 50 nm. [Claim 12] Optical component according to any one of the preceding claims. cédentes, characterized in that at least one of the layers of the stack of layers (2) is a nanostratified consisting of a multitude of layers having thicknesses between 2 nm and 10 nm, and that these layers are formed at least two alternating materials. [Claim 13] Optical component (10) according to any one of the preceding claims, characterized in that the substrate (1) and the stack of layers (2) are at least partially transparent in the spectral range of infrared and visible. [Claim 14] Optical component according to any one of the preceding claims, characterized in that the substrate and the stack of layers are at least partially transparent in at least one, preferably in a plurality and in particular in all the wavelength ranges following: - in the wavelength range from 400 nm to 650 nm; - at one or more wavelengths in the range from 1000 nm to 1600 nm; - in the wavelength range from 3,500 nm to 5,000 nm; - in the wavelength range from 7,500 nm to 12,000 nm. [Claim 15] Optical component (10) according to any one of the preceding claims, characterized in that the substrate (1) consists of zinc sulfide or zinc selenide. [Claim 16] Optical component (10) according to any one of the preceding claims, characterized in that the layer of the second type (3) consists of a material chosen from the group comprising hafnium oxide (HfO ₂ ), the oxide scandium (Sc ₂ O ₃ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), yttrium oxide ( Y ₂ O ₃ ), titanium oxide (TiO ₂ ), aluminum oxide (A1 ₂ O ₃ ), cerium oxide (CeO ₂ ) and mixtures thereof. [Claim 17] Optical component (10) according to any one of the preceding claims, characterized in that the additional layer (5) is a layer of fluoride. [Claim 18] Optical component (10) according to the preceding claim, characterized in that the additional layer (5) consists of a fluoride chosen from the group comprising barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (NdF ₃ ), ytterbium fluoride (YbF ₃ ), magnesium fluoride (MgF ₂ ), aluminum fluoride (A1F ₃ ), dysprosium fluoride (DyF ₃ ), yttrium fluoride (YF ₃ ) and mixtures thereof. [Claim 19] Optical component (10) according to any one of the preceding claims, characterized in that the upper layer (3) is applied by a process different from the other layers of Γ layer stack (2). [Claim 20] Optical component (10) according to any one of the preceding claims, characterized in that the stack of layers (2) comprises a sequence of alternating layers which comprises at least one other layer made of the same material as one of the three layers higher. [Claim 21] Optical component (10) according to any one of the preceding claims, characterized in that the lower layer (9) is a layer of the third type of layer having the lowest refractive index. [Claim 22] Optical component (10) according to any one of the preceding claims, characterized in that the stack of layers (2) comprises a total number of layers which is between seven and thirty. [Claim 23] Optical component (10) according to any one of the preceding claims, characterized in that the optical component shows no visible sign of surface scratches after a wiper test according to the test standard TS1888, and that the amount of surface defects according to ISO 10110 is preferably reduced by at least 20% compared to an optical component with a fluoride layer as the upper layer. [Claim 24] Method of manufacturing an optical component (10) with an anti-reflective coating, characterized in that a substrate (1) is provided with a stack of layers (2), comprising a plurality of successive layers of different materials and with indices of different refraction, which constitutes an anti-reflective coating in which the layers of the stack of layers (2) are deposited successively from at least three different materials or combinations of materials, so that the stack of layers produced by the deposition successive comprises at least one layer of a first type, of a second type and of a third type, with at least three different refractive indices, a layer of the first type having a refractive index greater than that of a layer of the second type, and a layer of the third type having a lower refractive index than that of a layer of the second type; and in which an upper layer and a second upper layer are provided, the upper layer (7) being a layer of the second [Claim 25] [Claim 26] [Claim 27] type (3), and the second upper layer being a layer of the first type (4) and therefore having a refractive index which is higher than the refractive index of the layer superior; and in which the stack of layers (2) comprises at least one other layer which is arranged under the two upper layers in the stack of layers (2) and which is a layer of the third type (5) and therefore has a refractive index which is lower than the refractive indices of the two upper layers. Method according to the preceding claim, characterized in that the layer of the second type (3) is applied by a method chosen from the group comprising ion plating, ion implantation, ion assistance / advanced plasma, magnetron sputtering, ion beam spraying, cathode arc deposition and atomic layer deposition. Method according to the preceding claim, characterized in that the layer of the second type is applied in the form of two sublayers (11, 12), in that the second sublayer (11) is applied without an ionic or plasma support process , and in that the first undercoat (12) is applied using an ionic or plasma support method Use of the optical component (10) in a visible domain with a single or multispectral spectrum and in the infrared domain of the electromagnetic spectrum.